Apparatus and method for optical time domain reflectometry

ABSTRACT

An optical signal routing device may include a first lens, second lens and a wavelength division multiplexer (“WDM”) filter positioned between the first and second lenses. The WDM filter may reflect a signal of a first wavelength with a first attenuation and pass the first wavelength signal attenuated by at most a second attenuation to the second lens, the first attenuation exceeding the second attenuation by a first predetermined amount. The WDM filter may reflect a signal of a second wavelength different than the first wavelength with at most a third attenuation, the first attenuation exceeding the third attenuation by at least a second predetermined amount. The device may further include a reflector positioned to reflect the first wavelength signal reflected by the WDM filter toward the WDM filter with at least a fourth attenuation, the fourth attenuation exceeding the second attenuation by at least a third predetermined amount.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 14/873,594, filed on Oct. 2, 2015, which claims the benefit of thefiling date of U.S. Provisional Patent Application No. 62/060,541 filedOct. 6, 2014, the disclosures of which are both hereby incorporated byreference herein.

BACKGROUND

In optical transmission systems, cables, such as fiber-optic cables, areused to transmit information. In some systems, such as that shown inFIG. 1, cables 15 and 15 a-d extend from an optical line terminal(“OLT”) 10 to one or more optical network units (“ONUs”) 20 a-d. Anoptical signal(s) of a certain wavelength or group of wavelengths,indicated in the figure as λi, is transmitted downstream (downstreamsignal) from the OLT 10 to the ONUs 20 a-d via the cables 15 and 15 a-d.An optical signal of a certain wavelength or group of wavelengths,indicated in the figures as λj, is transmitted upstream (upstreamsignal) from the ONUs 20 a-d to the OLT 10.

If damage occurs to one or more of the cables 15 and 15 a-d, for examplea break in a cable from inclement weather, rodents or otherwise, it maybe desirable to determine the location of the fault (or break) along thecable, such that the cable may be repaired.

One way to determine the location of the break in the cable is shown inFIG. 2. An optical time-domain reflectometer (“OTDR”) 30 is installedcoupled to the portion of the optical fiber cable 15 located near theOLT 10, and an OTDR signal reflector 40 a-d is installed coupled to theportion of the optical fiber cable 15 a-d located near each ONU 20 a-d.An optical signal of a certain wavelength or group of wavelengths,indicated in the figure as λk, is sent downstream along the cables 15and 15 a-d to the ONUs 20 a-d from the OTDR 30, and the OTDR signalreflectors 40 a-d are configured to reflect the λk signal upstreamtoward the OLT 10, such that the reflected signal λk may be detected bythe OTDR 30. If a break or fault occurs in the cable upstream of theOTDR reflector 40 a-d, and downstream of the point at which the cable 15extending from the OLT 10 is joined with individual optical cables 15a-d extending respectively to the ONUs 20 a-d, the λk signal will not bereflected back to the OTDR 30 by the OTDR reflector 40 a-d, which isdownstream of the break. The distance between the OTDR 30 and each OTDRsignal reflector 40 a-d is very accurately known and stored in adatabase, such that based upon the information of the distanceassociated with each OTDR reflector 40 a-d and the lack of a reflectedλk signal from a particular OTDR signal reflector 40 a-d associated witha corresponding ONU 20 a-d, it may be possible to determine in whichcable 15 a-d between an ONU 20 a-d and the point at which the multiplecables 15 a-d extending to the respective ONUs 20 a-d are joined to thesingle cable 15 extending from the OLT 10 the fault is located.

Examples of known OTDR signal reflectors 40 a-d are shown in FIGS. 3 and4. For example, in FIG. 3 an OTDR signal reflector 40 a is shown as aBragg grating 41 a in an optical fiber cable 15 a. In FIG. 4, an OTDRsignal reflector 40 a is shown as a thin film wavelength divisionmultiplexer (“WDM”) filter 42 a. Each OTDR signal reflector 40 a isdesigned to allow λi and λj signals to pass therethrough with no orminimal attenuation, such that the λi and λj signals are transmittedbetween the OTL 10 and ONUs 20 a-d with no or minimal degradation orpower loss, while almost completely or completely reflecting the λksignals with minimal attenuation. However, in practice, some portion ofthe λi and λj signals incident on the OTDR signal reflector 40 a-d isreflected. In particular, the reflection of the λi signals upstreamtoward the OTDR 30 is undesirable because such reflected λi signals maycause crosstalk or interference.

Therefore, it would be desirable, when performing OTDR in an opticalnetwork to detect cable faults or breaks, to provide a device thatmaximizes reflection of the λk signal while minimizing any reflection ofother signals, such as the λi and/or λj signals, thereby increasing theaccuracy with which an OTDR may help determine the particular locationof a fault in an optical fiber cable of the optical network.

BRIEF SUMMARY

According to a first embodiment of the disclosure, an optical signalrouting device may include a first lens positioned for receiving anoptical signal, a second lens, and a wavelength division multiplexer(“WDM”) filter positioned between the first and second lenses. The WDMfilter may be configured to reflect a signal of a first wavelength withat least a first attenuation, for example about 15 dB, and pass thesignal of the first wavelength attenuated by at most a secondattenuation, for example about 1 dB, to the second lens. The firstattenuation may exceed the second attenuation by at least a firstpredetermined amount. The WDM filter may be further configured toreflect a signal of a second wavelength different than the firstwavelength with at most a third attenuation, for example about 1 dB. Thefirst attenuation may exceed the third attenuation by at least a secondpredetermined amount. A reflector may be positioned to reflect thesignal of the first wavelength reflected by the WDM filter toward theWDM filter with at least a fourth attenuation, for example about 15 dB.The fourth attenuation exceeding the second attenuation by at least athird predetermined amount.

The reflector may be a mirror configured to reflect the signal of thesecond wavelength toward the WDM filter with at most a fifthattenuation, for example about 3 dB. The reflector may alternately be awavelength selective reflector. The first attenuation may exceed thefifth attenuation by at least a fourth predetermined amount. An opticalfilter may be positioned between the WDM filter and the reflector. Theoptical filter may be configured to pass the signal of the secondwavelength attenuated by at most a sixth attenuation, for example about1 dB, and to pass the signal of the first wavelength attenuated by atleast a seventh attenuation, for example about 15 dB. The firstattenuation may exceed the sixth attenuation by at least a fifthpredetermined amount, and the seventh attenuation may exceed the secondattenuation by at least a sixth predetermined amount.

According to a further embodiment of the disclosure, an optical signalrouting device includes a lens positioned for receiving an opticalsignal, a wavelength division multiplexer (“WDM”) filter, and areflector. The WDM filter may be positioned between the lens and thereflector. The WDM filter may be configured to pass a signal of a firstwavelength attenuated by at most a first attenuation, for example about1 dB, and to pass a signal of a second wavelength attenuated by at leasta second attenuation, for example about 15 dB. The second attenuationmay exceed the first attenuation by a first predetermined amount. Thereflector may be configured to reflect the signal of the firstwavelength toward the WDM filter with an attenuation of not more than athird attenuation, for example about 3 dB. The second attenuation mayexceed the third attenuation by a second predetermined amount. A firstoptical path may extend through the lens to the reflector, and a secondoptical path may extend from the WDM filter toward and through the lens,the first optical path being different from the second optical path.

The reflector may be a mirror configured to reflect the signal of thesecond wavelength toward the WDM filter with an attenuation of not morethan the third attenuation, for example about 1 dB. An optical filtermay be positioned adjacent the lens. The optical filter may beconfigured to pass the signal of the second wavelength attenuated by notmore than a fourth attenuation, for example about 1 dB, and to pass thesignal of the first wavelength attenuated by at least a fifthattenuation, for example about 15 dB. The fifth attenuation may exceedthe fourth attenuation by a third predetermined amount.

Alternately, the reflector may be a wavelength selective reflector andconfigured to reflect the signal of the second wavelength with at leasta fourth attenuation, for example about 15 dB, wherein the fourthattenuation exceeds the first attenuation by a third predeterminedamount. An optical filter may be positioned adjacent the lens. Theoptical filter may be configured to pass the signal of the secondwavelength attenuated by not more than a fifth attenuation, for exampleabout 1 dB, and to pass the signal of the first wavelength attenuated byat least a sixth attenuation, for example about 15 dB. The sixthattenuation exceeds the fifth attenuation by a fourth predeterminedamount.

According to a further embodiment of the disclosure, an optical signalrouting device may include a first lens positioned for receiving anoptical signal, a second lens, and a wavelength division multiplexer(“WDM”) filter positioned between the first and second lenses. The WDMfilter may be configured to pass, to the second lens, a signal of afirst wavelength attenuated by at most a first attenuation, for exampleabout 1 dB, and a signal of a second wavelength attenuated by at least asecond attenuation, for example about 15 dB. The second attenuation mayexceed the first attenuation by a first predetermined amount. Areflector may be positioned to reflect the signal of the firstwavelength, passed by the WDM filter to the second lens, toward the WDMfilter with not more than a third attenuation, for example about 3 dB.The second attenuation may exceed the third attenuation by a secondpredetermined amount. A first optical path may extend through the firstand second lenses to the reflector, and a second optical path may extendfrom the WDM filter toward and through the first lens, the first opticalpath being different from the second optical path.

The reflector may be a mirror configured to reflect the signal of thesecond wavelength toward the WDM filter with an attenuation of not morethan the third attenuation, for example about 3 dB. An optical filtermay be positioned adjacent the first lens. The optical filter may beconfigured to pass the signal of the first wavelength from the WDMfilter attenuated by at least a fourth attenuation, for example about 15dB, and to pass the signal of the second wavelength reflected from theWDM filter attenuated by less than a fifth attenuation, for exampleabout 1 dB. The fourth attenuation may exceed the fifth attenuation by athird predetermined amount.

Alternately, the reflector may be a wavelength selective reflector andconfigured to reflect the signal of the second wavelength passed by theWDM filter by at least a fourth attenuation, for example about 15 dB.The fourth attenuation may exceed the first attenuation by a thirdpredetermined amount. An optical filter may be positioned adjacent thefirst lens, the optical filter configured to pass the signal of thefirst wavelength from the WDM filter attenuated by at least a fifthattenuation, for example about 15 dB, and to pass the signal of thesecond wavelength reflected from the WDM filter attenuated by less thana sixth attenuation, for example about 1 dB. The fifth attenuation mayexceed the sixth attenuation by a fourth predetermined amount.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 show optical systems according to the prior art.

FIG. 5 is a schematic view of a system according to one embodiment ofthe invention.

FIG. 6 shows graphs of characteristics of a WDM filter that may be usedwith the system of FIG. 5.

FIG. 7 shows graphs of characteristics of wavelength selectivereflectors (mirrors) that may be used with the system of FIG. 5.

FIG. 8 is a schematic view of a system according to another embodimentof the invention.

FIG. 9 shows graphs of characteristics of a WDM filter that may be usedwith the system of FIG. 8.

FIG. 10 is a schematic view of a system according to a furtherembodiment of the invention.

FIGS. 11-12 are diagrams of wavelength selective reflectors (mirrors)that may be used with the embodiments described herein.

FIGS. 13A-C are schematic representations of alternative embodiments ofthe wavelength selective reflector of FIG. 10.

DETAILED DESCRIPTION

FIG. 5 shows a schematic view of a system according to an embodiment ofthe disclosure. This embodiment may be generally similar to the overallsetup described above in connection with FIG. 2, and further includes adevice 100 arranged in an optical path extending from the OLT 10 to theONU 20 a-d. The device 100 may include a first mechanical connection 110(e.g. a ferrule), a first lens 120, a wavelength division multiplexing(WDM) filter 130, a second lens 140, and a second mechanical connection150, arranged in sequence, such that an optical signal λi entering thedevice 100 via optical fiber F1 at the first mechanical connection 110passes through the first lens 120, the WDM filter 130 and the secondlens 140 then exits through optical fiber F3 at the second mechanicalconnection 150 to continue toward the ONU 20 a-d, along the opticalpath, with very minimal attenuation. The device 100 may further includea wavelength selective reflector (mirror) 170 arranged in relation tothe first lens 110, an optical second filter 160 and the WDM filter 130,such that a second optical path extends from the reflector 170, throughthe optical second filter 160 via optical fiber F2, through the firstlens 120 and to the WDM filter 130. The optical signal transmission andreflection characteristics of the WDM filter 130 and the selectivereflector 170 may provide that λi signals from the OLT 10 are reflectedby the WDM filter 130 with attenuation of about 15 dB toward theselective reflector 170, which then reflects the reflected λi signalswith additional attenuation of about 15 dB to the WDM filter 130, whichthen may reflect the λi signals reflected from the reflector 170upstream, out of the device 100, toward the OLT 10 with furtherattenuation of about 15 dB. In addition, the optical signal transmissionand reflection characteristics of the WDM filter 130 and the selectivereflector 170 may provide that λk signals from the OLT 10 are reflectedby the WDM filter 130 with minimal attenuation, e.g. about 1 dB, towardthe selective reflector 170, which then reflects the reflected λksignals with minimal attenuation toward the WDM filter 130, which thenmay reflect the λk signals reflected from the reflector 170 upstream,out of the device 100, toward the OLT 10 with minimal attenuation. It isnoted that the optional second filter 160 may further significantlyattenuate, e.g., by about 15 dB, the λi signals passing therethrough,while only minimally attenuating, e.g., by about 1 dB, the λk signalsthat pass therethrough. The characteristics of optical filter 160 may besimilar or identical to those shown in the graphs of FIG. 9.

Accordingly, in the embodiment described in connection with FIG. 5, inthe device 100, the WDM filter(s) 130 passes λi and λj signals withminimal loss, but provides that any portion of the λi and λj signalsthat is reflected is significantly attenuated (e.g., 15 dB). Thewavelength selective reflector 170 allows reflectance of the λk signalwithout much loss and reflects the λi signal with substantialattenuation. Therefore, the signal reflected to the WDM filter 130 fromthe wavelength selective reflector 170 includes the λk signal, which hasbeen minimally attenuated, and the λi signal that has been substantiallyattenuated, e.g., by about 30 dB, before the reflected λi signal isfurther attenuated (15 dB) when reflected by the WDM 130 filter to exitthe device 100 towards the OTDR 30. In this embodiment, in the secondoptical path, the λi signal is substantially attenuated at least 3times, whereas the λk signal experiences minimal attenuation. The λksignal may be further isolated with respect to the λi signal in thesecond optical path with the use of the optional second filter 160described above and shown, or with further optional filters.

It should be understood that, although described as a wavelengthselective reflector, the wavelength selective reflector 170 may be asimple mirror reflecting all wavelengths. In this case, although the λksignal will not be attenuated differently from the λi signal whenreflected by the simple mirror, the other elements in the second path ofthe device 100 may provide sufficient selective attenuation of the λisignal so that a signal exiting the device 100 at the fiber F3 anddetected by the OTDR 30 includes the λk signal which is still highlyisolated from other signals in the signal exiting the device 100 at theconnector 110.

Graphs of transmittance versus wavelength and reflectance versuswavelength for the WDM filter 130 of FIG. 5 are shown in FIG. 6. Graphsof reflectance versus wavelength for the wavelength selective reflector170 of FIG. 5 are shown in FIG. 7. The graph on the left of FIG. 7 showsselected wavelengths where reflectance is high and low, while the graphon the right shows where a simple mirror is used reflecting allwavelengths more or less equally. In one example, the wavelengths of λi,λj, and λk are in a range of between about 1260 nm and about 1671 nm. Inthis example, the wavelengths of the signals λi and λj passing throughdevice 100 may be between about 1260 nm and about 1618 nm, while thewavelengths of the signal λk may be between about 1639 nm and about 1671nm. The insertion loss of the device 100 for signals having wavelengthsbetween about 1260 nm and about 1618 nm (e.g. λi and λj) passing throughthe device 100 may be less than about 1 dB. The signals havingwavelengths between about 1639 nm and about 1671 nm (e.g., λk) exitingthe device 100 at the connector 110 may be further isolated by greaterthan about 40 dB with respect to other signals exiting the device at theconnector 110. The insertion loss of the device 100 for signals havingwavelengths between about 1639 nm and about 1671 nm (e.g. λk) enteringand exiting the device 100 at the connector 110 may be less than about 4dB. The signals having wavelengths between about 1260 nm and about 1618nm (e.g. λi, λj) exiting device 100 at the connector 150 may be furtherisolated with respect to λk signals by greater than about 40 dB. Signalspassing through device 100 may also have a polarization dependent loss(“PDL”) which may be below about 0.15 dB for the device 100. Similarly,signals passing through device 100 may have a polarization modedispersion (“PMD”) of less than about 0.2 picoseconds.

The fibers F1 extending from OLT 10 to device 100, F3 extending fromdevice 100 to ONU 20 a-d, and F2 extending from lens 120 via connector110 to selective reflector 170 may each be, for example, angled orotherwise configured to have a return loss greater than 55 dB and mayinclude anti-reflective coating. The fibers may be, for example, of thefiber type G.652D, G.657A1/A2 and/or G.657B2/B3. The first and secondlenses 120, 140, may also be angled or otherwise configured for a returnloss greater than 55 dB and may include anti-reflective coating. Themechanical connectors 110 and 150 may provide support to the fibers. Asnoted above, the WDM filter 130, which may take any suitable form suchas a chip or filter-on-lens, may be configured to pass λi and λj signalswith minimum attenuation while reflecting λk signals with minimumattenuation. Preferably the spectrum settings for λi, λj, λk are suchthat there is no spectral overlap among λi, λj, and λk.

For device 100, λi signals may experience an insertion loss of less thanabout 1 dB when passing from fiber F1 to fiber F3, λk signals may befurther isolated with respect to λi signals by greater than about 50 dBfrom fiber F1 to fiber F3, and the return loss of both λi and λk signalsmay be greater than about 55 dB from fiber F1 to fiber F3. Similarly, λjsignals passing from fiber F3 to fiber F1 may experience an insertionloss of less than about 1 dB. Further, signals passing from fiber F1 toand through fiber F2, and reflecting back to and through fiber F2 andthen to fiber F1 may have the following properties. The insertion lossof λk signals passing from fiber F1 to and through fiber F2 to thereflector 170 may be less than about 0.5 dB, and λi signals may befurther isolated with respect to λk signals by greater than about 20 dBwhen passing from fiber F1 to and through fiber F2 to the reflector 170.Signal λk passing from fiber F2 to reflector 170 and back to fiber F2may experience an insertion loss less than about 3 dB, and λi signalsmay be further isolated with respect to λk signals greater than about 20dB for this same optical path. It should be understood that signalswhich are supplied from the fiber F2 and are reflected toward fiber F2may not be further isolated significantly if reflector 170 is a simplemirror. Further, λk signals from the reflector 170 that pass to andthrough fiber F2 to the fiber F1 may experience an insertion loss ofless than about 0.5 dB, and λi signals may be further isolated withrespect to λk signals by greater than about 20 dB for that same path.With the example described above, the total insertion loss experiencedby the λk signal entering device 100 through fiber F1 and exiting thedevice 100 through fiber F1 may be less than about 4 dB, and the λksignal may be further isolated with respect to the λi signal for thesignal exiting the device 100 at the connector 110 by greater than about60 dB. However, as should be understood, the further isolation of the λksignal with respect to the λi signal for the signal exiting the device100 at the connector may be less if reflector 170 is a simple mirror,and may be greater if the λi signal passes through an optional opticalsecond filter 160 as the signals pass from fiber F1 to and through fiberF2 and then again through and from fiber F2 to fiber F1.

As described above, device 100 (as well as devices 200 and 300 describedbelow) may provide for further isolation of the λk signal with respectto other signals exiting the device 100 at the connector 110 by greaterthan 40-60 dB, whereas the isolation of prior art systems described inconnection with FIGS. 2-4 may be about 35-40 dB less than that of thetechnology of the disclosure. Device 100 may be provided as a singleunit, for example as shown within the dashed outline of FIG. 5. In oneexample, device 100 may be provided within a cylindrical stainless steelhousing having a diameter of less than about 3.5 mm and a length of lessthan about 80 mm.

In some examples, the fiber optic cables used with device 100 may have abare fiber diameter of approximately 250 microns in a tight bufferedconstruction with a 900 micron thick cable jacket, although other sizecable jackets may be suitable, for example 1.2 mm, 2.0 mm, 2.9 mm, etc.The fibers may terminate at any suitable connector, for example SC, LC,FC, MU, ST, E2000, or any other suitable connector.

FIG. 8 shows a schematic view of another embodiment of the invention.This embodiment may be generally similar to the overall setup describedabove in connection with FIG. 2, and further includes a device 200arranged in an optical pathway extending from the OLT 10 to the ONU 20a-d. The device 200 may include a mechanical connection 210 for couplingto a first fiber cable F4 extending from OLT 10, a first lens 220, a WDMfilter 230, and a wavelength selective reflector 270 arranged insequence, where the connection 210 is also for coupling to a secondfiber cable F5 extending to the ONU 20 a. In this case, while thewavelength selective reflector 270 may have similar characteristics towavelength selective reflector 170 described in connection with FIG. 5,the WDM filter 230 has different characteristics than those described inconnection with WDM filter 130 of FIG. 5. As shown in FIG. 9, thecharacteristics of transmission and reflectance of this WDM filter 230are such that λk signals are passed through the device 200 nearlywithout attenuation and with minimal reflection, while λi and λj signalsare reflected nearly completely with minimal attenuation and also passedwith substantial attenuation. Referring again to FIG. 8, the signal fromthe OLT 10 may enter the device 200 via fiber cable F4 at the connection210, pass through the lens 220 and then to the WDM filter 230 along athird optical path F7 of the device 200. At the filter 230, the λisignal is nearly completely reflected along another different fourthoptical path F8 of the device 200, which fourth path F8 extends throughthe lens 220 and the mechanical connection 210, which is coupled to thefiber cable F5 that extends to the ONU 20 a. In addition, a portion ofthe λi signal passes through the WDM filter 230, which substantiallyattenuates (e.g., about 25 dB) such λi signal portion, toward thewavelength selective reflector 270, which reflects such λi signalportion with significant attenuation of about 25 dB. This reflected λisignal portion is further significantly attenuated (about 15 dB) whenpassing through the WDM filter 230 after which the reflected λi signalportion travels along the optical path F7 (through the lens 220 andconnector 210) and exits the device 200 through the fiber cable F4extending to the OTDR 30. In contrast, the λk signal, which passesnearly completely through the WDM filter 230 without much attenuation,is reflected nearly completely by the wavelength selective reflector 270without much attenuation, and such reflected λk signal passes throughthe WDM filter 230, without much attenuation, and then may travel alongthe path F4 through the lens 220 and the mechanical connection 210,where the reflected λk signal may be coupled into and be conveyedthrough the fiber cable F4 extending to the ODTR 30. Similar to device100, device 200 provides that signals λi reflected toward the OTDR 30 bythe device 200 are greatly attenuated in relation to the λk signal,which is reflected toward the OTDR 30 with minimal attenuation. However,the mechanisms are reversed in terms of the transmittance andreflectance of the WDM filter 230 as shown in the drawings. As withdevice 100, the wavelength selective reflector 270 of device 200 may bea simple mirror, or it may selectively reflect signals to help furtherisolate the λk signal from other signals exiting the device 200 at thefiber F4. In addition, an optional optical filter 260, having thecharacteristics as shown in the graphs of FIG. 6, may be positionedbetween lens 220 and connector 210 in the path F8 and pass λi or λjsignals without significant attenuation, such as at most 1 dB, and passλk signals with about 15 dB more attenuation than the attenuation of theλi or λj signals, to provide additional isolation of the λk signals withrespect to the λi or λj signals exiting the device at the connector 210.

It should be understood that although WDM filter 230 (as well as WDMfilters 130, 330) is shown as a single filter, in practice dual filtersmay be used in place of a single WDM filter. WDM filter 230 is alignedwith respect to lens 220 to couple the optical path F7 extending fromcable fiber F4 to the optical path F8 extending to cable fiber F5. Inother words, WDM filter 230 is not perpendicular to the optical pathcoming from fiber cable F4. Reflector 270 is aligned to reflect opticalsignals in the optical path extending from cable fiber F4 into the sameoptical path and towards the cable fiber F4.

FIG. 10 shows a schematic view of another embodiment of the disclosure.In this embodiment, device 300 is similar to device 200 with certainvariations. In particular, device 300 includes a first mechanicalconnector 310, first lens 320, WDM 330, and optional filter 360 in asimilar configuration to device 200. However, compared to device 200, inthe device 300, a second lens 340 and a second mechanical connector 350are disposed between the wavelength selective reflector 370 and the WDM330, arranged such that optical signals from cable fiber F6 pass throughthe WDM 330 to the reflector 370 through the second lens 340, the secondconnector 350 and cable fiber F10 extending from the connector 350 tothe reflector 370 in sequence. The optical signals which pass throughthe WDM 330 and arrive at the reflector 370 are reflected by thereflector 370 toward the second connector 350, and such reflectedsignals are routed to the WDM 330 through the cable fiber F10, thesecond connector 350 and the second lens 340, and then along opticalpath F 6 through the first lens 320 and first mechanical connector 310to the cable fiber F64 to exit the device 300 via cable fiber F6. Withthis configuration, λi and λj signals may be reflected without muchattenuation by WDM filter 330 to exit the device 300 respectively at thefibers F8 and F6 extending to the ONT 20 a and OLT 10, such that λi andλj signals pass through the device 300 to their intended destinationwithout much attenuation. Any λi and λj signals that pass through WDMfilter 330 pass through cable fiber F10 and are either reflected withsignificant attenuation by reflector 370 or pass through reflector 370with significant attenuation, unless reflector 370 is a simple mirror.λk signals pass through WDM filter 330 with little attenuation and arecompletely or almost completely reflected by reflector 370 with minimalattenuation. To the extent any λk signals are reflected by WDM filter330 along the path F11 extending therefrom toward cable fiber F8,additional filter 360, which has characteristics similar to filter 260,may additionally attenuate the reflected λk signal. As with WDM filter230, WDM filter 330 may not be perpendicular to the optical pathextending from cable fiber F6, but rather arranged to reflect a signalfrom the fiber F6 traveling along the path of fiber F6 towards and alongthe optical path F11 extending to the cable fiber F8, while reflector370 may be perpendicular to the optical path extending coextensive withthe cable fiber F10.

One embodiment of a structure for use as a wavelength selectivereflector, such as wavelength selective reflector 370, is shown in FIG.11. Effectively, the end of fiber cable F10 is cleaved, preferably at 90degrees relative to a longitudinal axis L of the cable F10 along whichoptical signals are expected to be conveyed (along the fiber core 402inside fiber cladding 404), and reflective material, such as that usedto fabricate a mirror, is coupled, adhered, coated, or otherwiseattached to the end of the cable F10 so as to form a reflective surface410 nearly perfectly or perfectly perpendicular to the expected opticalsignal beam path along the axis. As in the other embodiments above, thefilter mirror 410 may be a simple mirror reflecting all wavelengthsincluding λk signals or may be specific to reflect a signals, such as bypassing λi and λj signals from cable F10 almost in their entiretytherethrough without much attenuation and/or by reflecting a veryminimal portion of the λi and λj signals through the fiber core 402.FIG. 12 shows another embodiment where the end of fiber cable F10 iscoupled to a lens device 420, which has characteristics similar to themirror surface 410 of FIG. 11.

Referring again to FIG. 10, first connector 310 may be, for example, afiber capillary to provide support to cable fibers F6 and F8, with anend of first connector 310 being angled, for example about 8 degrees,and include an anti-reflective coating to reduce or eliminate reflectionof λi, λj, and λk signals as they exit or enter cable fibers F6 and F8.Connectors 110 and 210 may take similar forms as connector 310. Optionalfilter 360 may take the form of a WDM filter directly coated or adheredon first lens 320 in the optical path extending to cable fiber F8.Optional filter 360 may alternately take the form of a WDM filterdirectly coated or adhered on first connector 310 in the optical pathextending to cable fiber F8. If optional filter 360 is used, it may alsotake the form of a dual WDM filter combining both examples describeddirectly above. WDM filter 330 may take a similar form, with one filterdirectly coated or adhered to first lens 320, one filter directly coatedor adhered to second lens 340, or both. Lenses 320 and 340 may begradient-index (“GRIN”) lenses, for example with ends facing opticalpaths respectively extending from the fiber cables F6 (for lens 320) andF10 (for lens 340) angled at approximately 8 degrees with little or noangle on the opposite end of the lens facing WDM filter 330. The ends ofthe lenses 320 and 340 may include anti-reflective coating to reduce oreliminate reflection of λi, λj, and λk signals as they exit or enter thelenses.

Still referring to FIG. 10, second connector 350 may be, for example, afiber capillary to provide support to cable fiber F10, with an end ofsecond connector 350 facing second lens 340 being angled, for exampleabout 8 degrees, and treated with an anti-reflective coating to reduceor eliminate reflection of λi, λj, and λk signals as they exit or entercable fiber F10. The other end of second connector 350 may beperpendicular to the optical path of fiber F10 and may be treated with afilter mirror (for example by coating or adhering) so that the end ofcable fiber F10 and filter mirror 370 are within or part of secondconnector 350, as shown in FIG. 13A. Alternately, connector 350 may besplit into separate pieces. As shown in FIG. 13B, connector portion 350a may include the angled and coated surface, with fiber cable F10extending into another connector portion 350 b with the reflector 370positioned at an end thereof. Still further, as shown in FIG. 13C, fibercable F10 may extend beyond the end of connector 350 and the reflectorapplied directly to the fiber cable F10, similar to the configurationshown in FIG. 11.

Although devices 100, 200, and 300 are illustrated herein as coupling asingle upstream optical fiber to a single downstream optical fiber, thedevices 100, 200, and 300 may alternately couple to two or more upstreamoptical fibers and a corresponding number of downstream optical fiberswithout requiring additional lenses, filters, etc., with the onlylimitation being the space available in the devices 100, 200, and 300 toconnect to and/or house the optical fibers. This may provide additionalfunctionality at reduced cost by limiting the numbers of lenses andmechanical connections needed. For example, in such embodiments,additional pairs of optical fibers and optical paths may be added usingcapillaries or ferrules with multiple holes, where the same lens pairsis used.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent disclosure. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present disclosure.

The invention claimed is:
 1. An optical signal routing devicecomprising: a first lens positioned for receiving an optical signal; awavelength division multiplexer (“WDM”) filter; and a reflector, the WDMfilter positioned between the first lens and the reflector, the WDMfilter configured to pass a first portion of a signal of a firstwavelength attenuated by at most a first attenuation relative to thesignal of the first wavelength and reflect a second portion of thesignal of the first wavelength attenuated by at least a secondattenuation relative to the signal of the first wavelength, the secondattenuation exceeding the first attenuation by at least a firstpredetermined amount, and the WDM filter being further configured topass a third portion of a signal of a second wavelength different thanthe first wavelength attenuated by at least a third attenuation relativeto the signal of the second wavelength and to reflect a fourth portionof the signal of the second wavelength attenuated by at most a fourthattenuation relative to the signal of the second wavelength, wherein thethird attenuation exceeds the first attenuation by at least a secondpredetermined amount, wherein the reflector is positioned to reflect afifth portion of the first portion of the signal of the first wavelengthtoward the WDM filter, in which the fifth portion is attenuated by atmost a fifth attenuation relative to the first portion, wherein thethird attenuation exceeds the fifth attenuation by at least a thirdpredetermined amount.
 2. The device of claim 1, wherein the firstattenuation is about 1 dB, the third attenuation is about 15 dB, and thefifth attenuation is about 3 dB.
 3. The device of claim 1, wherein thereflector is a mirror configured to reflect a sixth portion of the thirdportion of the signal of the second wavelength toward the WDM filter, inwhich the sixth portion is attenuated by at most a sixth attenuationrelative to the third portion, the third attenuation exceeding the sixthattenuation by at least a fourth predetermined amount.
 4. The device ofclaim 3, further comprising an optical filter positioned adjacent thefirst lens, the optical filter configured to pass a seventh portion ofthe fourth portion of the signal of the second wavelength attenuated byat most a seventh attenuation and to pass an eighth portion of thesecond portion of the signal of the first wavelength attenuated by atleast an eighth attenuation, wherein the eighth attenuation exceeds theseventh attenuation by at least a fifth predetermined amount.
 5. Thedevice of claim 1, wherein the reflector is a wavelength selectivereflector and configured to reflect a sixth portion of the third portionof the signal of the second wavelength toward the WDM filter, with atleast a sixth attenuation relative to the third portion, wherein thesixth attenuation exceeds the first attenuation by at least a fourthpredetermined amount.
 6. The device of claim 5, further comprising anoptical filter positioned adjacent the first lens, the optical filterconfigured to pass a seventh portion of the fourth portion of the signalof the second wavelength attenuated by at most a seventh attenuation andto pass an eighth portion of the second portion of the signal of thefirst wavelength attenuated by at least an eighth attenuation, whereinthe eighth attenuation exceeds the seventh attenuation by a fifthpredetermined amount.
 7. The device of claim 1, wherein a first opticalpath extends through the first lens to the reflector, and a secondoptical path extends from the WDM filter toward and through the firstlens, the first optical path being different from the second opticalpath.
 8. The device of claim 1, further comprising a second lenspositioned between the WDM filter and the reflector.
 9. The device ofclaim 8, wherein a first optical path extends through the first andsecond lenses to the reflector, and a second optical path extends fromthe WDM filter toward and through the first lens, the first optical pathbeing different from the second optical path.